The present invention is directed generally to methods for determining unauthorized use of a radio-frequency based telephone system and in particular to a method and system for determining if a unauthorized clone of a mobile telephone has been made and is in use.
In almost all wireless communications systems, a base station must determine the user of a mobile unit for billing or monitoring purposes. But without the fixed structure of a wired communications system, the base station of a wireless communications system generally must determine the user solely on the identification received from the mobile unit. In present day cellular mobile telephone systems, this identification is usually in the form of a mobile identification number (MIN) and/or an electronic serial number (ESN). Each mobile unit has associated with it a unique MIN and/or an ESN in addition to the typical "telephone dialing number". The MIN/ESN is used in the setup of communications between the control channel and the mobile unit but is generally not known or readily discernible without sophisticated electronic equipment or access to telephone company records.
To determine the user, a base station often compares the identification received from the mobile unit with the identifications of authorized mobile telephones stored in a database. The database may be stored locally at the base station or may include databases stored throughout a coverage area. Once the identified user is determined to be authorized to use the system, the base station may allow the mobile unit to receive or place a call. A mobile unit, which the base station allows to receive or place a call, is an "authorized mobile unit."
Unfortunately, it is known for detecting devices to monitor the airwaves used by mobile telephones for the purpose of detecting and intercepting the identification information associated with authorized mobile units. The intercepted identification information may then be stored into a "clone" mobile unit. Because the clone mobile unit uses the same identification data as an authorized mobile unit, a base station wrongly believe that the close unit is an authorized unit and will incorrectly allow the second mobile to receive or place a call. Significantly, the base station will bill or monitor the user of the first (authorized) mobile unit for the calls of the clone (unauthorized) mobile unit, causing considerable confusion as to the authenticity of any of the calls to or from the authorized mobile unit and permitting unbilled use of the telephone network.
In one proposed solution to this problem, a base station randomly or periodically attempts to identify two or more mobile units with the same identification. In such a system, the base station may periodically transmit an audit (or control) message on the control channel. If more than one response is received by the base station (or by other interconnected base stations), the base stations know that at least one of these mobile units is a clone unit. This proposed solution, however, does not address two additional problems: (1) most unauthorized mobile units are "turned off" when not in use; and (2) periodic or random transmissions on a control channel consumes appreciable bandwidth on the control channel. Indeed, to be effective the periodic transmission should occur fairly frequently, thus consuming more bandwidth to become more effective.
Accordingly, it is an object of the present invention to provide a novel wireless communication system for eliminating the problems and burdens of the prior art.
It is another object of the present invention to provide a novel wireless communication system for identifying unauthorized mobile units during the highest probability period that unauthorized mobile units are "turned on."
It is another object of the present invention to provide a novel wireless communication system for identifying unauthorized mobile units without overburdening the base station or the control channels.
It is another object of the present invention to provide a novel wireless communication system for identifying unauthorized mobile units when connecting a call to or from a mobile unit.
It is yet another object of the present invention to provide a novel wireless communication system for identifying unauthorized mobile units in a local loop system.
It is still another object of the present invention to provide a novel wireless communication system for identifying unauthorized mobile units in a cellular system.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.